1. Field of the Invention
This invention relates to ink supply cartridges for ink jet printers and more particularly to disposable ink cartridges which supply the ink to thermal ink jet printheads integrally mounted thereon.
2. Description of the Prior Art
Ink jet printing systems are usually divided into two basic types, continuous stream and drop-on-demand. In continuous stream ink jet printing systems, ink is emitted in a continuous stream under pressure through one or more orifices or nozzles. The stream is perturbed, so that it is broken into droplets at determined, fixed distances from the nozzles. At the breakup point, the droplets are charged in accordance with varying magnitudes of voltages representative of digitized data signals. The charged droplets are propelled through a fixed electrostatic field which adjusts or deflects the trajectory of each droplet in order to direct it to a specific location on a recording medium, such as paper, or to a gutter for collection and recirculation. In drop-on-demand ink jet printing systems, a droplet is expelled from a nozzle directly to the recording medium along a substantially straight trajectory that is substantially perpendicular to the recording medium. The droplet expulsion is in response to digital information signals, and a droplet is not expelled unless it is to be placed on the recording medium. Except for periodic concurrent expulsion of droplets from all nozzles into a receptacle to keep the ink menisci in the nozzles from drying, drop-on-demand systems require no ink recovering gutter to collect and recirculate the ink and no charging or deflection electrodes to guide the droplets to their specific pixel locations on the recording medium. Thus, drop-on-demand systems are much simpler than the continuous stream type.
There are two basic propulsion techniques for the drop-on-demand ink jet printers. One uses a piezoelectric transducer to produce pressure pulses selectively to expel the droplets and the other technique uses thermal energy, usually the momentary heating of a resistor, to produce a vapor bubble in the ink, which during its growth expels a droplet. Either technique uses ink-filled channels or passageways which interconnect an orifice or nozzle and an ink-filled manifold. The pressure pulse may be generated anywhere in the channels or the manifold. However, the bubble generating resistor (hence the name bubble jet) must be located in each channel near the nozzle.
The thermal ink jet printers, sometimes referred to as bubble jet printers, are very powerful because they produce high velocity droplets and permit very close nozzle spacing for printing higher numbers of spots or pixels per inch on the recording medium. The higher the number of spots per inch, the better the printing resolution, thus yielding higher quality printing.
In thermal ink jet printers, printing signals representing binary digital information originate an electric current pulse of a predetermined time duration in a small resistor within each ink channel near the nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a vapor bubble. The ink at the orifice is forced out as a propelled droplet by the bubble. At the termination of the current pulse, the bubble collapses and the process is ready to start all over again as soon as hydrodynamic motion or turbulence of the ink stops. The turbulence in the channel generally subsides in fractions of milliseconds so that thermally expelled droplets may be generated in the kilohertz range. For more detailed explanation of the operation and construction of a thermal ink jet printer refer to copending U.S. application Ser. No. 588,166 to W. G. Hawkins filed on Mar. 9, 1984 now U.S. Pat. No. 4,532,530.
Existing thermal ink jet printers usually have a printhead mounted on a carriage which traverses back and forth across the width of a stepwise movable recordng medium. The printhead generally comprises a vertical array of nozzles which confronts the recording medium. Ink-filled channels connect to an ink supply reservoir, so that as the ink in the vicinity of the nozzles is used, it is replaced from the reservoir. Small resistors in the channels near the nozzles are individually addressable by current pulses representative of digitized information or video signals, so that each droplet expelled and propelled to the recording medium prints a picture element or pixel.
Typical thermal ink jet printers encounter several problems. Constant predetermined ink pressure at the nozzles has to be maintained, while the level of ink in the supply reservoir is changing as the ink is spent. To prevent ink from contaminating the front face of the printhead, because of ink weeping from the nozzles, a slight negative pressure is required. Also, the ink in the nozzles has to be isolated from pressure transients generated in the reservoir by the carriage motion, and whenever more than one nozzle is used, crosstalk between nozzles must be prevented. By crosstalk it is meant that the activation of one nozzle to propel a droplet therefrom causes an undesired effect on a droplet expelled from an adjacent nozzle, such as a change in its size, velocity or direction. Any of these changes in droplet parameters cause defective printing or impact print quality. Several approaches to the solution of these problems are evident in the prior art, as delineated below, but none have entirely solved them.
U.S. Pat. No. 4,463,362 to Thomas discloses an ink jet printing system having baffle plates in a movable reservoir accommodating a plurality of print heads. The plates prevent the printing ink from sloshing back and forth during movement of the reservoir to ensure that a supply of ink is maintained in the flexible supply tubes to the printheads.
Japanese patent application No. 54-117503 filed Sept. 12, 1979 and published without examination on Apr. 16, 1981 discloses a thermal drop-on-demand ink jet printer having a printhead and ink reservoir combination movably mounted on a carriage. The reservoir is partitioned into an upper chamber adjacent the printhead and a lower chamber. The upper chamber is supplied from the lower chamber by a small tube by capillary force.
Austrian patent specification No. 212,039 published Nov. 25, 1960 discloses an ink reservoir with a baffle that partitions the reservoir into two sections. The ink is supplied through a tube by the differences of heights of ink levels in the two sections.
U.S. Pat. No. 4,306,245 to Kasugayama et al discloses an ink jet printing arrangement having a movable integral printhead and ink reservoir wherein the printhead is fed ink through a tube from the reservoir by capillary action. The ink in the reservoir is maintained at atmospheric pressure and may have a filter to pass air but not liquid.
U.S. Pat. No. 4,342,041 to Kasugayama et al discloses an ink jet printer of the type having a printhead mounted on a carriage and adapted for reciprocation. The printer has two ink reservoirs. One small reservoir is integrally formed with the printhead and the main large reservoir is fixedly mounted at a different location. A flexible supply hose connects the two reservoirs and the hose is adapted to swing about a fixed point during carriage reciprocation. As a result of this swinging motion, the ink in the supply hose is subjected to a centrifugal force which produces a pumping effect that automatically supplies ink from the main reservoir to the small one. Since the capacity of the ink reservoir that is integral with the printhead is extremely small, the change of weight on the carriage is negligible as the ink is consumed. Therefore, there is caused no change of carriage running speed by weight change, when a linear motor is used as the carriage driving motor. Also, bubbles transported from the main reservoir are dissipated in the small reservoir since both are vented to atmosphere.
U.S. Pat. No. 4,383,263 to Ozawa et al discloses several embodiments of a drop-on-demand ink jet printing system. The printhead is integral with a sub-tank which is connected to a suction means and a main tank. The sub-tank is maintained at a negative pressure and a tube feeds ink to the printhead from the bottom of the sub-tank.
U.S. Pat. No. 3,708,798 to Hildenbrand et al discloses an ink jet printer having a collapsible ink supply bag that supplies ink to a printhead at a constant pressure through a manifold with an air bubble trap. The manifold is capable of manual venting and is interconnected to the printhead by hoses.
U.S. Pat. No. 4,456,916 to Kocot discloses an ink jet printer having a reciprocating printhead. A disposable cartridge forms part of the printhead and includes a nozzle and a multicompartment ink reservoir. One reservoir compartment supplies ink to the nozzle. A float in one compartment is periodically actuated to force ink over a wall that forms the different compartments to maintain the proper height in the one that supplies ink to the nozzle to replenish the ink used.